Electrorefining of zirconium



United States Patent ELECTROREFINING 0F ZIRCONIUM William w. Gullett, College Park, Md., assignor to Chi- No Drawing. Application Qctober 17, 1957 Serial No. 690,611

1 Claim. c1. 204--64) This invention relates to electrorefining of zirconium. It relates particularly to refining in electrolytes composed of fused alkalinous metal chlorides, that is, alkali or alkaline earth metal chorides or mixtures of them, having dissolved therein zirconium chlorides. I have found that zirconium oxide which is formed by the solution of crude zirconium containing oxygen is not substantially soluble in such electrolytes and hence the cathode deposit is not contaminated by oxygen from the anode.

I have found that the electrolytic bath must contain at least one lower chloride of zirconium in solution in the bath. The bath is defined by a series of equilibria as follows:

I have found that Reaction may be practically disregarded and that the bath to be useful for refining must correspond primarily to Reaction 2 and that Reaction 4 must be prevented from running from right to left by which the bath would be converted into finely divided Zr and ZrCl, which would volatilize.

This is accomplished by a low concentration of ZrCl a low temperature and increased pressure.

I have found that at atmospheric pressure, a concentration of dissolved zirconium in a lower valence state of 1-2% is preferable and that a suitable alkalinous metal bath is composed of 65% SrCl and 35% NaCl. This electrolyte melts at a comparatively low temperature and does not break into two layers.

It is necessary in carrying out the refining to avoid increased local concentrations of dissolved lower chlorides of zirconium. This is preferably accomplished by anodic solution from a small surface which is vibrated to prevent concentration polarization.

In anotherembodiment of the invention, Reaction 4 is forced from right to left by pressure and a large surface of the Zr to be refined, and a cathode is placed at minimum distance from the dissolving Zr so that the reaction cycle of solution diffusion and disproportionation is re duced by deposition on the cathode before the concentration for disproportionation takes place.

The electrolytic bath for my invention may be made in a number of ways. One of the preferred ways is heating Zr, PbCl SrCl and NaCl in a closed tube to about 800 C. The preferred proportions are 1 mole of Zr to 1 of Pbcl with the eutectic proportions of SrCl and NaCl so as to obtain a 5% concentration of Zr in the electrolyte. Such an electrolyte will contain about 2% Zr as lower chlorides.

This electrolyte may be used at low temperatures and relatively high pressures, or it may be heated to 800 C. at atmospheric pressure with vibrated Zr strips in the 2,927,067 Patented Mar. 1, 1960 bath to partly reduce ZrCL; present and in part to distill it off. i i

In another procedure for preparing an electrolytic bath for my inventionjl add ZrCl and sodium inarnounts corresponding to ZrCl in small increments to SrCl: in a pot heated to 600 C. provided with a condenser which can be cleared by rodding. The product-of this operation was a n'ii 'ture'ot ZrClg, Zr'CI ZrCl NaCl and sodium.

This mass could be melted at 750 C.. under 25 lbs. argon pressure and used as an electrolytic bath in which the zirconium in it served as a disperse anode, the pot which carried the anodic current being very close to the cathode which was preferably preformed to provide a layer of salt with dispersed fine crystals.

Having now described my invention in its most general terms, I will illustrate it by examples.

Example I In this example, I take 900 grams of Zr scrap and mix it with 2780 grams of PbCl and 18,000 grams of an eutectic mixture of SrCl and NaCl and seal in a heavy iron tube. I heat to 800 C. for 2 hours, I open the iron tube and recover about 2080 grams of lead in a button and 15,020 grams of fused salt containing chlorides of zirconium and a little lead chloride. I melt this mixture in an iron pot 2 in diameter in an argon atmosphere at 1000 C., add 100 grams; ZrO and vibrate a zirconium strip in it for 15 minutes. I then cool to 750 C. and allow the solids to settle.

I now place zirconium scrap analyzing 370% O in a hollow iron anode chamber 1 inch in diameter with small openings below the bath, place this at the center of the pot and vibrate this to provide anodic solution.

I now place the removable iron liner in the potas cathode and electrolyze at 10 amperes for 10 hours. I remove the cathode by raising into an argon atmosphere and on cooling, I remove the coarse crystalline product and wash with 2% HCl. 100 grams of zirconium was recovered, which when melted in argon had a Brinell hardness of 80.

The structure of the cathode deposit was a zirconium plate on the cathode, a thin layer of salt with fine zirconium crystals and an outer layer of crystal intergrowths constituting more than of the cathode product.

Example 11 In this example, I take 2300 grams ZrCl and 920 grams of sodium and add them in small increments to a pot at 700 C. provided with a condenser. I rod the condenser frequently to clear it of sublimed ZrCL; which falls in the reaction pot. the start 3000 grams SrCl When reaction is complete, I cool the mass in an argon atmosphere, and break it out of the pot. tube 2" in diameter and provided with a centrally disposed iron rod cathode insulated from the tube. A cover is provided to withstand 50 lbs. pressure having a packing gland and lock for the cathode, an argon inlet and a lock for adding comminuted crude zirconium. The cathode can be lifted into the cool upper portion of the tube and removed and replaced through a suitable lock.

When the lower portion of the tube has been heated to I 750 C. under 50 lbs. pressure, 10 amperes is passed for I place in the bottom of the pot at I place this mass in a heavy walled Inconel 3 The structure of the cathode deposit in this example was like that described for Example 1.

What is claimed is:

The process of electrorefining crude zirconium which consists in making it a disperse anode in an electrolyte at 700-900 C. under a pressure above atmospheric in a fused bath of the reaction product of one mole zirconium tetrachloride with approximately two moles of sodium in strontium chloride at 500-700 C., having an inert cathode closely spaced to said disperse anode and passinga unidirectional current from said anode to said cathode whereby to form pure coarse crystalline zirconium on the cathode.

References Cited in the file of this patent UNITED STATES PATENTS Ferrand Nov. 17, 1936 Schultz et al Feb. 14, 1956 Guillette May 22, 1956 Raynes Feb. 19, 1957 Dean Mar. 12, 1957 Dean Dec. 24, 1957 Gullett Dec. 24, 1957 Wainer Jan. 28, 1958 Dean June 10, 1958 Olson July 29, 1958 OTHER REFERENCES Electrolytic Titanium, Chicago Development Corp. 

